问题

I am not good at JavaScript and have been trying to get Ivan Kuckir's Fastest Gaussian Blur code to work with no success. When I load the page, it becomes unresponsive so that I will have to close the window somehow. The code I use follows. What am doing wrong?

<html>
<head>
<script src="Path_To_GaussianBlur.js"></script>
</head>

<body>
<img id="sourceImage" src="SomeImage_200px_x_200px.jpg" />
<canvas id="canvas1" width="200" height="200" style="border: 1px solid blue"></canvas>
<canvas id="canvas2" width="200" height="200" style="border: 1px solid red"></canvas>

<script>
    document.getElementById("sourceImage").onload = function () {

        var c1 = document.getElementById("canvas1");
        var c2 = document.getElementById("canvas2");

        var ctx1 = c1.getContext("2d");
        var ctx2 = c2.getContext("2d");

        var img = document.getElementById("sourceImage");

        ctx1.drawImage(img, 0, 0);
        ctx2.drawImage(img, 0, 0);

        var source = ctx1.getImageData(0, 0, c1.width, c1.height);
        var target = ctx2.getImageData(0, 0, c2.width, c2.height);

        for (var i = 0; i < source.data.length; i += 4) {
            // red chanel
            gaussBlur_4(source.data[i], target.data[i], c1.width, c1.height, 2);
            // green channel
            gaussBlur_4(source.data[i + 1], target.data[i + 1], c1.width, c1.height, 2);
            // blue channel
            gaussBlur_4(source.data[i + 2], target.data[i + 2], c1.width, c1.height, 2);
        }

        ctx2.putImageData(target, 0, 0);
    };
</script>
</body>
</html>

回答1:

As stated in comments you need to split the rgba array into separate channels. You can do this in several ways, here is one:

Split

var idata = ctx.getImageData(0, 0, w, h), // assumes ctx/w/h to be defined
    rgba = idata.data,
    len = w * h,
    rSrc = new Uint8Array(len),           // source arrays
    gSrc = new Uint8Array(len),
    bSrc = new Uint8Array(len),
    aSrc = new Uint8Array(len),
    // define target arrays the same way as above
    i = 0, offset = 0;

for(; i < len; i++) {
  rSrc[i] = rgba[offset++];
  gSrc[i] = rgba[offset++];
  bSrc[i] = rgba[offset++];
  aSrc[i] = rgba[offset++];
}

Now you can pass each of those arrays to the blur function using target arrays set up in a similar manner as the source arrays, then merge back the result to rgba format.

Apply

gaussBlur_4(rSrc, rTrg, w, h, radius);
gaussBlur_4(gSrc, gTrg, w, h, radius);
gaussBlur_4(bSrc, bTrg, w, h, radius);
gaussBlur_4(aSrc, aTrg, w, h, radius);

Additional tip: if you're using images (as in photos) you can skip blurring the alpha channel as there is none (or technically, is fully opaque in canvas).

Merge

To merge, simply do:

for(i = 0, offset = 0; i < len; i++) {
  rgba[offset++] = rTrg[i];
  rgba[offset++] = gTrg[i];
  rgba[offset++] = bTrg[i];
  rgba[offset++] = aTrg[i]; // or just increase offset if you skipped alpha
}

ctx.putImageData(idata, 0, 0);

Due to license conflict on SO a running example can be found in this fiddle (and here is an alternative split/merge using 32-bits approach).

来源：https://stackoverflow.com/questions/37503847/fastest-gaussian-blur-not-working

标签

javascript